104 ELEMENTARY GEOLOGY 
traced to another group (the sedimentary), the meta- 
morphic rocks are characterized by a crystalline struc- 
ture. In some cases this causes them to closely 
resemble the igneous rocks, with which they might 
easily be confused, if it were not for the fact that 
they usually differ from these by the presence of a 
decided banding or, foliation (Fig. 46).' 
Since they are crystalline, there would be little danger 
of confusing most of them with the sedimentary rocks, 
notwithstanding the fact that they have a banding 
something like sedimentary stratification. This band- 
ing, however, is quite different from stratification, for 
it is an arrangement of crystalline minerals, while 
that of the sedimentary rocks is usually either a band- 
ing of fragments, arranged according to size, or else of 
differently colored layers. The metamorphic strata 
result from complex changes of other rocks. In these 
changes, the elements are often made to combine in 
a new manner. Given the same assemblage of ele- 
ments, whether in a shale or a lava, the changes of 
metamorphism will produce the same results. Hence 
a schist may be formed either from a shale or a lava; 
therefore in highly altered rocks the original state 
can no longer be detected. 
1 Of course the rather rare flow structure (p. 70) of some of the igneous 
rocks may cause confusion ; but when this is present distinctly enough to be 
seen, one can detect the evidence of liquid flow, which proves that the rock 
was once molten, and hence igneous. 
